Evaluation of Geotechnics, Seismicity and Tectonic Processes to Characterize Possible Geohazards in Menengai Geothermal Project Field.

Abstract

Menengai geothermal project area is situated within a closed volcanic system of a relatively young caldera which seems that can still be tectonically activated by agents associated with geotechnics and seismicity. Topography of caldera floor is highly rugged following intensive lava flows from post caldera eruptions. Over thirty (30) geothermal wells have already been drilled on floor caldera within an approximate surface area of 4 km2 largely at the central area of the caldera. Even though the near surface is observed to be geotechnically suitable for foundations of constructions and infrastructure, deep-seated processes are bound to destabilize and affect the geothermal development program. Probable geohazards are observed to affect geothermal reservoir within the caldera, productivity of drilled wells, and stability of caldera floor to hold buildings, steam gathering system and infrastructures. This study has observed that caldera floor can be subdivided into five (5) main caldera compartments; SE, SW, NE, NW and NNW formed by sub-sequential subsidence due to tectono-volcanic induced processes with down-throws influenced by either Molo or Solai TVA related structures within the caldera. The compartments are defined by major fault-scarps (N-S and E-W) which appear to be main conduits of cold in-flows to the geothermal wells and reservoir. Geothermal wells are concentrated within a tectonically less stable NW Compartment; this may enhance further landmass movements at depth following increased seismicity from a combination of frictional forces being exerted by steam-jets from discharging wells at one-go during geothermal production stage. Geothermal development plan and layout on surface constructions and infrastructure dominate slopes within NW Compartment thus categorized as high risk going by the amount of investment being put in place. Possible geohazards in Menengai Geothermal Project are observed to be as a result of integrated failures related to geotechnics, seismicity and tectonic processes due to occur within the caldera.